In a gas turbine, hot gases of combustion flow from an annular array of combustors through a transition piece for flow along an annular hot gas path. Turbine stages are typically disposed along the hot gas path such that the hot gases of combustion flow from the transition piece through first-stage nozzles and buckets and through the nozzles and buckets of follow-on turbine stages. The turbine buckets may be secured to a plurality of turbine wheels comprising the turbine rotor, with each turbine wheel mounted to the rotor shaft for rotation therewith.
A turbine bucket generally includes an airfoil having a pressure side and a suction side and extending radially upward from a horizontal, substantially planar platform. A hollow shank portion extends radially downward from the platform and may include a dovetail or other means to secure the bucket to a turbine wheel. The bucket platform generally defines the inner flow path boundary of the combustion products flowing through the hot gas path. Accordingly, due to the high temperatures of the combustion products and mechanical loading on the bucket, the platform may be an area of high stress concentrations. In order to alleviate a portion of the thermally induced stress, a turbine bucket may include some type of platform cooling scheme or arrangement to reduce the temperature differential between the top and bottom of the platform.
Various platform cooling arrangements are known in the art. For example, a known cooling arrangement includes a plurality of film cooling holes defined in a turbine bucket between the shank portion and the platform. Cooling air is introduced into the hollow cavity of the shank portion and is directed through the film cooling holes to cool the platform in the localized region of the holes. However, it has been found that such film cooling provides less than optimal cooling for the bucket platform and also requires the use of an excessive amount of air. Another known cooling arrangement includes a cored platform, wherein the platform defines a cavity through which cooling medium may be supplied. However, a cored platform provides limited design flexibility for improving the performance of the cooling arrangement. Moreover, the process of forming the cored platform can be both expensive and difficult to accomplish.
Accordingly, a cooling arrangement for a turbine component, such as a turbine bucket, that effectively cools the component's platform and that is relatively easy to manufacture would be accepted in the technology.